In recent years the automotive industry witnessed a significant increase in the amount of electronic systems being introduced into their products. Different communication systems have been developed for the operation of the various Electronic Control Units (ECUs). A communication system in general comprises a number of units or nodes, which communicate with each other. The communication is usually done via a bus, which logically connects several nodes over the same set of wires. Each node consists of a host-controller, a Communication Controller and a physical device generating data. The Communication Controller transmits data received by the Host Controller and supplies received data to the Host Controller.
Different bus systems are known in the art. The LIN-Bus (Local Interconnect Network) is a bus-system used within current automotive network architectures. It is designed for mechatronic applications in cars and is a small and rather slow network system. The integrated members are intelligent sensor devices or actuators. One dedicated node is set up as a LIN Master, all other attached nodes are the LIN Slaves. This topology is fixed and cannot be changed afterwards.
A faster network is the Controller Area Network (CAN), a multicast shared serial bus standard originally developed in the 1980s for connecting electronic control units. CAN was specifically designed to be robust in noisy environments and is a network for enabling any device to communicate and work with any other device or network without creating a great strain on the bus. In automotive applications it is used, e.g., for air condition control units, seat actuators, centralized door locking systems or acceleration skid control. In addition to CAN networks, many vehicles use additional LIN buses for smaller subnetworks.
However, the introduction of advanced control systems combining multiple sensors, actuators and electronic control units are beginning to place demands on the communication technology that are not currently addressed by existing communication protocols. For a wire replacement of mechanical and hydraulic braking and steering systems imposing stringent requirements in reliability and survivability distributed fault tolerant computer systems are mandatory. Moreover, safety-relevant applications require real-time data management. A high priority message must be transmitted in a predefined amount of time in all situations. Flexibility in both bandwidth and system extension are also key attributes as the need for increased functionality and on-board diagnostics also increase. Advanced control systems have begun to place boundary demands on the existing CAN communications bus.
The FlexRay system has been proposed to fulfil the demand for a bus system with a deterministic and error-tolerant communication and a high data rate of up to 10 Mbit/s. It is highly flexible regarding changes of a network configuration. In contrast to current event-triggered communication protocols such as CAN, FlexRay combines a time-triggered along with an event-triggered system. At the core of the FlexRay system is the FlexRay communications protocol. The protocol provides flexibility and determinism by combining a scalable static and dynamic message transmission, incorporating the advantages of familiar synchronous and asynchronous protocols. The protocol supports fault-tolerant clock synchronization via a global time base, collision-free bus access, message oriented addressing via identifiers, scalable system fault-tolerance via the support of either single or dual channels.
The FlexRay controller comprises a transmitter and receiver unit for each of its channels, where each transmitter and receiver unit can also be separated into two independent units, a timing unit, a controller host interface (CHI) for connection to the host and a protocol state machine. Extracted data or data for transmission are stored in buffers. The FlexRay architecture levels comprise a host level, a controller host interface level, a protocol engine level, a channel interface level and a topology level with possible channels A and B. Data transmitted through the controller host interface includes status data, control data, e.g. external clock synchronization, message data or configuration data related to the network or node configuration.
EP 1355456 discloses the FlexRay protocol. A network system with a least one node coupled to a communication line and with means for communication, which are able to create a communication cycle on said communication is provided.
The communication cycle is the fundamental element of the media access scheme within FlexRay. It is defined by means of a timing hierarchy. The timing hierarchy consists of four timing hierarchy levels as depicted in FIG. 1. The highest level, the communication cycle level, defines the communication cycle. It contains the static segment, the dynamic segment, the symbol window and the network idle time (NIT). The next lower level, the arbitration grid level, contains the arbitration grid that form the backbone of FlexRay media arbitration. In the static segment the arbitration grid consists of consecutive time intervals, called static slots, in the dynamic segment the arbitration grid consists of consecutive time intervals, called minislots.
WO 2005/002145 discloses an assembly and method for managing a memory that is accessed by a Communication Controller and a host processor of a network node in a network. The assembly and method are preferably applied to a FlexRay bus system. An identifier is assigned to each data message, and a number of buffers that corresponds to the number of relevant identifiers are provided in the memory of a network node. Control data is stored in at least some of the buffers that have been assigned to the identifiers.
WO 2004/105328 describes a message memory for a communication protocol and method, applicable to CAN or FlexRay systems. Using a combination of a virtual memory representation and a physical memory divided into a specific number of segments as a message memory, the memory allows optimisation for specific use in an application in terms of the quantity of message objects and their data capacity.
Modern communication systems like FlexRay are specifically designed for fault-tolerance and flexibility. A disadvantage of the existing solutions is that configuration data and buffer data are handled through dedicated logic inside the Communication Controller such that any access to this data has to be handled though a Communication Controller access slave port. Such dedicated logic inside the controller puts a constraint on the configuration space of the network and defines a maximum number of buffers thus providing an upper limit to the flexibility of the communication system.